Influenza is a highly transmissible respiratory virus that causes an average of 114,000 hospitalizations and 36,000 deaths in the United States each year. It is of particular concern today because of the potential for an avian influenza pandemic. Transmission of influenza among patients and employees in healthcare settings is still common because immunization rates among healthcare workers are low, and employees often continue to work with respiratory illnesses. During outbreaks in nursing homes, illness rates greater than 60% have been reported. A better understanding of the role of various modes of transmission of influenza virus is needed to better plan and allocate resources during the recurring annual influenza outbreaks and to prepare for a possible pandemic. The objective of our study is to characterize the size and quantity of aerosol droplets produced by humans while coughing, and then uses this information to better understand the mechanisms by which influenza is transmitted from infected individuals to others. This objective will be accomplished using well-established experimental and theoretical techniques in conjunction with laboratory experiments and actual clinical studies. The specific aims are: (I) Characterize aerosol production by coughing. A measurement system will be used to characterize cough-generated aerosols from human subjects, and the ability of surgical masks and N95 respirators to block the dissemination of cough- generated aerosols will be evaluated. (II) Study the dissemination of virus-laden aerosols produced by coughing. A commercial live attenuated influenza vaccine will be used as a surrogate to study airborne viral transmission in the laboratory. Laboratory experiments will also be used to validate and improve a prototype two-stage bio-aerosol sampler and PCR-based virus detection system. The sampler will then be used to study the spread of influenza in a healthcare facility, where selected workers will be monitored during the months of high influenza activity. (Ill) Develop a computer model of the aerosol generation and dispersion. Computer models based on physical principles will be developed and utilized to complement the experimental work. The modeling work will build upon preliminary work performed by the P.I. that is closely related to the subject of this work. A hierarchy of models ranging from one-dimensional steady to three dimensional transient simulations will be utilized and validated against experimental results. [unreadable] [unreadable] [unreadable]